Download Inverse multiplexing of digital data

US006205142B1
(12) United States Patent
(10) Patent N0.:
Vallee
(54)
US 6,205,142 B1
(45) Date 0f Patent:
INVERSE MULTIPLEXING OF DIGITAL
FOREIGN PATENT DOCUMENTS
DATA
0 584 398
.
.
96/08120
(75) Inventor: Richard Vallee, Gatmeau (CA)
96/17489
(73) Assignee: Nortel Networks Limited (CA)
( * ) Notice:
Mar. 20, 2001
3/1994 (EP).
3/1996
WO
.
6/1996 EWO; '
OTHER PUBLICATIONS
Subject to any disclaimer, the term of this
Palmer’ “hfverse Multiplexing (if ATM Cells Over LOW
patent is extended or adjusted under 35
Speed PNI S Such as T1 and
U_S_C_ 154(k)) by 0 days'
Sathe, ATM Inverse Multiplexing Mechanism , (1994).
’ (1994)‘ _
”
* cited by examiner
(21) Appl' NO‘: 08/909’060
(22) Filed;
Aug, 14, 1997
Primary Examiner—Alpus H. Hsu
(74) Attorney, Agent, or Firm—Finnegan, Henderson,
FaraboW, Garrett & Dunner, L.L.P.
Related US. Application Data
(57)
(60)
Provisional application No. 60/024,023, ?led on Aug. 16,
(51)
1996'
Int. Cl.7 ............................. .. H04J 3/02; H04L 12/56
(52)
(58)
US. Cl. ........................ .. 370/394; 370/395; 370/471;
370/536
Field of Search ................................... .. 370/389 394
370/395 400 408 465 470 471’ 474’
476 477’ 506 536 542’ 543’ 544;
’
(56)
’
’
’
’
’
ABSTRACT
In ATM networks, digital data in ATM cells are sent to a
destination node Over more than One transmission link in
round robin fashion This is Called inverse multiplexing At
connection start-up, the source node informs the destination
node of the Speci?c round robin fashion of the transmission
links so that the ATM cells are reassembled in a proper
sequential order. Inverse multiplexing control cells are used
to communicate betWeen the source node and destination
References Cited
node for connectivity testing of transmission links. Cell
U-S~ PATENT DOCUMENTS
stuf?ng is also provided in one embodiment to accommodate
non-synchronized links among transmission links. In a par
5 285 441 *
2/1994 Bansal et al. ...................... .. 370/228
?cular embodimenh two Consecutive Control Cells indicate a
5’6O8’733
3/1997 Vance et aL
stu?ing cell. A start-up procedure is described When not all
5:617:417 *
4/1997 Sathe et al. ........................ .. 370/394
5,875,192 *
2/1999
370/394
the transmission links are usable
Cam et al. ......................... .. 370/474
5,970,067 * 10/1999 Sathe et al. ........................ .. 370/394
OCTET
1-5
74 Claims, 14 Drawing Sheets
FIELD
ATM CELL HEADER
6
IMA LABEL
7
CELL ID, LINK ID
8
IMA FRAME SEQUENCE NUMBER
9
ICP CELL OFFSET
10
LINK STUFF INDICATION
11
STATUS & CONTROL CHANGE INDICATION
12
Tx IMA ID
13
Rx IMA ID
14
GROUP STATUS & CONTROL
15
TX TEST CONTROL
16
Tx TEST PATTERN
17
Rx TEST PATTERN
18
LINK 0 INFORMATION
19
LINK 1 INFORMATION
20-49
LINK 2-31 INFORMATION
50-51
UNUSED
52-53
ORG-10
U.S. Patent
Mar. 20, 2001
Sheet 1 0f 14
US 6,205,142 B1
EmOPwD mz a
.QEN E.O5F2E‘
.GEv
NEOFwD mzwa
mwz a
U.S. Patent
Mar. 20, 2001
Sheet 2 0f 14
US 6,205,142 B1
BIT
8
7
6
5
4
3
2
1
VPI OR GFC
VPI
1
VPI
VCI
2
VCI
VCI
3
PT
CLP 4
HEC
5 |_
LLI
6 '6
O
CELL PAYLOAD
(48 OCTETS)
53
GFC:
VPI:
VCI:
GENERAL FLOW CONTROL
VIRTUAL PATH IDENTIFIER
VIRTUAL CHANNEL IDENTIFIER
PT:
CLP:
HEC:
PAYLOAD TYPE
CELL LOSS PRIORITY
HEADER ERROR CHECK
FIG. 3
PRIOR ART
U.S. Patent
Mar. 20,2001
Sheet 3 0f 14
US 6,205,142 B1
CE>L S
14
K AMA
CD
V12
LWM(#N
UNK#1 LWU(#2
/ /-1O AMA
ATM CEL S
FIG.4
U.S. Patent
Mar. 20, 2001
2#8$.59E038 802358%90 j8:m$0Iou?2/-08k3z5 8w5j@o92?m0p$5z
Sheet 4 0f 14
GEm
US 6,205,142 B1
2@$G8M5I0EBO 8:
.QEm
U.S. Patent
Mar. 20, 2001
Sheet 5 0f 14
OCTET
1
2
ALLOCATION
AIM-RDI
AIMFERR
3
4
AIMCSN(MSB)
AIMCSN(LSB)
5
6
R
R
7
R
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
45
46
47
48
R
R
R
CEC 1O
MSB: MOST SIGNIFICANT BYTE
LSB: LEAST SIGNIFICANT BYTE
FIG. 7
US 6,205,142 B1
U.S. Patent
OCTET
1-5
Mar. 20, 2001
Sheet 7 0f 14
US 6,205,142 B1
FIELD
ATM CELL HEADER
6
IMA LABEL
7
CELL ID, LINK ID
8
IMA FRAME SEQUENCE NUMBER
9
ICP CELL OFFSET
1O
LINK STUFF INDICATION
11
STATUS & CONTROL CHANGE INDICATION
12
TX IMA ID
13
RX IMA ID
14
GROUP STATUS & CONTROL
15
TX TEST CONTROL
16
TX TEST PATTERN
17
RX TEST PATTERN
18
LINK 0 INFORMATION
19
LINK 1 INFORMATION
20-49
LINK 2—31 INFORMATION
50-51
UNUSED
52-53
CRC-1O
FIG. 10
U.S. Patent
Mar. 20, 2001
I
START
Sheet 9 0f 14
US 6,205,142 B1
)
-START SENDING ICP CELLS OVER PROVISIONED LINKS
-INDICATE LINKS IN GROUP
-PROPOSE IMA ID AND FRAME LENGTH OVER ICP CELLS
-CHECK STATUS OF PROVISIONED INCOMING/OUTGOING LINKS
~
"
-STOP SENDING =
-SEND GROUP
GROUP ABORT
ABORT SIGNAL
SIGNAL
AT LEAST P
LINKS WITHOUT LINK
DEFECTS?
OVER ICP CELLS
-START TIME-OUT
TO SUSPEND
START-UP
A
-REJECT LINKS WITH LINK DEFECTS
-CONTINUE PROCEDURE WITH GOOD LINKS
-CHECK IMA FRAME LENGTH AND ADJUST IF NECESSARY
-CHECK IMA ID OVER GOOD LINKS
-ENSURE PROPER LINK CONNECTIVITY
AT LEAST P
LINKS PROPERLY
CONNECTED IN
GROUP?
-CHECK LDS FOR GOOD LINKS
AT LEAST P
RX LINKS IN
V
LDS?
FIG. 13a
U.S. Patent
Mar. 20, 2001
Sheet 10 0f 14
I
-SEND ICP CELLS WITH LDS BIT SET
FOR RX LINKS IN LDS
-LOOK FOR INCOMING ICP CELLS WITH
LDS SET FOR ALL TX LINKS
AT LEAST P
TX LINKS IN
LDS?
-SEND “READY" SIGNAL ON ALL ACCEPTED LINKS
AT LEAST P RX
LINKS READY?
ACTIVATE ALL READY LINKS AND
START SENDING ATM CELLS OVER THEM
FIG. 13b
FIG. 13a
FIG. 13b
US 6,205,142 B1
U.S. Patent
Mar. 20, 2001
Sheet 11 0f 14
LID=O
US 6,205,142 B1
_
LID-=0
IMA A
‘
IMA B
IMA C
IMA D
FIG. 15
U.S. Patent
Mar. 20, 2001
Sheet 12 0f 14
xmQmZbcm.
<QxmZvwp
mMOMm0.1Z5I_0>OP2
mwIxPzOZ]<
US 6,205,142 B1
U.S. Patent
Mar. 20, 2001
Sheet 13 0f 14
US 6,205,142 B1
V
V
FIG. 17
V
L|D=O
IMAA
~
IMAB
ID=1
ID=2
30
IMAC
IMAD
|D=1
L|D=0
‘
L|D=O
FIG. 18
;
|D=2
U.S. Patent
Mar. 20, 2001
Sheet 14 0f 14
US 6,205,142 B1
TIME
A
(1)
ICP
SICP
(2)
ICP
SICP
(3)
ICP
(4)
ICP
(5)
ICP
(6)
ICP
(7)
ICP
SICP
E
ICP
SICP
SICP
SICP
ICP
E
E
X
FIG. 19
US 6,205,142 B1
1
2
INVERSE MULTIPLEXING OF DIGITAL
DATA
control. The framing bit is used to determine relative link
delays While the link control bit is used for communication,
control and administration betWeen tWo TC points at tWo
ends of the inverse multiplexer.
This application claims bene?t to US. provisional
In order to establish the sequence of cells over the links
in a round robin manner, one end is de?ned as being
“master” and the other as “slave”. The “master” decides and
60/024,023 ?led Aug. 26, 1996.
FIELD OF THE INVENTION
informs the slave about the multiple link con?guration using
the control channel implemented through the link control
The invention relates to a neW mechanism for sending
ATM cells transparently over multiple sloWer transmission
links. In particular, the invention is directed to a method of
inverse multiplexing of a series of ATM cells transparently
10
over N transmission links (N being a positive integer) of
sloWer speed.
BACKGROUND OF THE INVENTION
15
It has been recogniZed that the T1/E1 rate (1544/2048
Mbit/s) is a cost effective Way of user access to an ATM
netWork as Well as connection betWeen ATM netWork
sWitches. HoWever, as ATM technology for Wide area net
Works is deployed more and more, demands for transmission
links of a rate higher than Tl/El are increasing. Links of
This protocol is only applicable, hoWever, for UNI appli
cation points because GFC bits that are robbed to implement
the TC layer are only present in a cell de?ned for UNI. For
NNI cells, the corresponding bits are no longer available
since they are captured under the VPI ?eld. Service provid
ers are interested in ATM inverse multiplexers for carrying
ATM traf?c at rates higher than Tl/El and loWer than T3/E3,
but this protocol Will not satisfy their need. It should also be
noted that the protocol calls for a need to identify a “master”
and a “slave” TC point and that requires an additional setting
to be performed by the netWork operator.
Bit Pipe Inverse Multiplexing
This protocol Was presented in “Physical Layer Sub
Working Group ATM Forum/94-0956, Inverse Multiplexing
higher rates, such as T3/E3 (44.736/34.368 Mbit/s), have
been designed to meet these needs. HoWever, the cost of
T3/E3 links is still prohibitive in many cases and the ratio of
cost versus realistic utiliZation of the entire rate is not alWays
attractive and fully justi?ed for neW ATM end users and
bits.
of ATM cells over loW speed UNIs such as T1 and E1”,
25
September 1994, by Digital Link Corporation. It proposes a
“bit pipe” inverse multiplexing technique requiring the
de?nition of a “bonding” (bandWidth on demand) like
service providers. ATM inverse multiplexers (AIMs) have
been proposed to satisfy the need by using multiple T1/E1
plexing.
links Which are grouped collectively to provide the service
It is not clear in the proposal hoW both ends of the links
exchange information concerning the order of cells to be
speci?cation for N (positive number) T1/E1 inverse multi
at a higher rate.
transferred from one end to another over multiple links. The
FIG. 1 and FIG. 2 shoW tWo sample con?gurations in
proposal mentions the existence and deployment of physical
Which AIMs are used. FIG. 1 depicts a user access to a
netWork through user netWork interfaces (UNIs) and FIG. 2
a link connection betWeen ATM sWitches through broadband
inter-carrier interfaces (BICIs) or private netWork to net
layer protocols that perform inverse multiplexing. The
inverse multiplexer Which can be used in this proposal is
35
Work interfaces (PNNIs).
1993”.
Referring to the ?gures, the basic function of AIMs is to
Work in pairs to take an ATM cell stream coming from the
The inverse multiplexing protocol de?ned in the above
user’s manual relies on the de?nition of an extra bit taken
ATM layer, send it over the multiple links by spreading cells
from Tl/El payload bits to con?gure the multiple links and
adjust differential link delays. This protocol introduces the
need for extra processing of data betWeen devices dealing
over the available links and ensure that the initial cell stream
can be retrieved at the far end. Thus the AIMs preferably
make the ATM traf?c transparent to the ATM layer over
multiple links Which connect them. As far as the ATM layer
is concerned, it should only see a pipe Whose rate is noW the
sum of the multiple link rates. It is assumed that each link
is run in clear-mode Without the presence of intermediate
ATM nodes processing ATM cells. This means that there
should be no cell discard by any intermediate transmission
With Tl/El frames and ATM cell delineation. It also causes
45
DSl/El Physical Layer speci?cations. Changes like this
providers Who are already using and deploying ATM equip
ment.
US. Pat. No. 5,608,733, Mar. 4, 1997, Vallee et al,
describes good Ways of obviating the above noted problems.
Currently no ATM inverse multiplexing protocols have
been proposed Which can properly interWork existing ATM
The patent uses ATM sequence number cells indicating a
speci?c round robin order of a plurality of transmission links
over Which ATM data cells are transmitted. The ATM
55 sequence number cells also indicate Whether or not a des
tination is ready to receive ATM data cells in that speci?c
round robin order.
NeW Transmission Convergence Protocol Using GFC Bits
This protocol Was presented in “Physical Layer Sub
Working Group ATM Forum/94-0775, ATM Inverse Multi
The present invention extends further variety of function
alities Which are useful in inverse multiplexing.
plexing Mechanism”, September 1994, by StrataCom Inc.
The protocol robs tWo of the Generic FloW Control (GFC)
bits contained in each cell transmitted over the multiple
Tl/El links to implement a neW transmission convergence
(TC) layer. FIG. 3 shoWs the ATM cell structure Which is
de?ned in the ITU Recommendation. The TC layer is
de?ned by one GFC bit for framing and the other one for link
the ATM cells to no longer be byte aligned With the DSl/El
frame. This is a requirement by the ATM Forum UNI
Would not be Welcome by end users, vendors and service
equipment.
inverse multiplexers or other ATM products Which are
already available on the market, and yet are ?exible enough
to ?t into the current standard ATM speci?cations. TWo
proposals for an ATM inverse multiplexing protocol have so
far been made and are described in detail beloW.
presumably the one de?ned by Digital Link Corporation in
their “DL3800 DSl Inverse Multiplexer Users Manual,
65
OBJECTS OF THE INVENTION
It is therefore an object of the invention to provide a
method of sending ATM traf?c over a connection consisting
of a plurality of transmission links.
It is another object of the invention to provide a method
of sending a series of ATM cells spread over a plurality of
transmission links in a speci?c round robin order.
US 6,205,142 B1
4
3
FIG. 5 shoWs preassigned cell header values for use by the
It is yet another object of the invention to provide a
method of sending ATM cells containing sequence numbers
physical layer;
therein over a plurality of transmission links in a speci?c
round robin order.
It is a further object of the invention to provide a method
of sending a series of ATM cells betWeen ATM inverse
multiplexers over a connection consisting of a plurality of
FIG. 6 shoWs a header pattern of an AIM OAM cell,
according to one embodiment of the invention;
FIG. 7 indicates allocation of OAM functions in the
information ?eld according to one embodiment of the inven
tion;
transmission links, transparent to the ATM layer.
It is yet another object of the invention to provide a
method of sending ATM traffic over a connection Which
consists of a plurality of transmission links and has been
10
recon?gured after the connection start-up.
It is still another object of the invention to provide an
ATM inverse multiplexing method Which is applicable to
UNIs, BICIs and PNNs.
It is a further object of the invention to provide a method
and demultiplexing of AIM OAM cells during transmission
15
of preserving link integrity by periodically sending sequence
number cells.
It is a further object of the invention to provide a method
of handling link failure and link recon?guration.
It is still a further object of the invention to provide a
method of stuffing cells to accommodate non-synchroniZed
links.
25
FIG. 16 shoWs the timing diagram of the test procedure of
the invention.
FIG. 17 illustrates looping of a test pattern at node B.
FIG. 18 depicts diagrammatically a scenario Where the
35
preceding the stuff event and the stuff ICP cells are cor
rupted.
nection consisting of a plurality of transmission links, said
data containing a series of ATM data cells. In particular, the
method comprises steps of identifying N number of trans
DETAILED DESCRIPTION OF PREFERRED
EMBODIMENTS
mission links over Which the series of ATM data cells are to
45
method further includes steps of receiving a series of inverse
multiplexing control cells Whose receive ready ?eld is set to
formed by P number out of N transmission links, P being a
It must adjust up to 32 milliseconds of differential link
delays betWeen individual links in a case Where T1/E1
positive integer smaller than N and ?nally sending each
ATM data cell in said series of ATM data cells in said second
links are used.
speci?c round robin order.
It must recon?gure multiple links in the event that a link
has to be added, deleted or is considered inadequate to
BRIEF DESCRIPTION OF THE DRAWINGS
55
provide service.
It must be de?ned for not only UNIs but also for PNNIs
and BICIs.
It must be transparent to the devices handling the con
vergence of ATM cells into the PDH signal.
It must be transparent to the devices dealing With ATM
for further objects and advantages thereof, reference may
noW be made to the folloWing description, taken in conjunc
tion With the accompanying draWings, in Which:
FIG. 1 shoWs a sample con?guration involving AIM
UNIs;
layer cells.
FIG. 2 shoWs a sample con?guration involving AIM
The present invention achieves all of the above require
ments and solves the problems discussed earlier. The inven
BICIs or PNNIs;
FIG. 3 depicts the ATM cell structure de?ned in the ITU
FIG. 4 is a schematic illustration of multiplexing and
demultiplexing of ATM cells over AIMs and links;
There are requirements that have to be considered When
de?ning a neW ATM inverse multiplexing protocol. These
requirements are:
It must multiplex and demultiplex an ATM cell stream
distributed in a round robin manner over multiple links
such as T1/E1 links.
indicate a second speci?c round robin order in a group
Recommendation;
test pattern procedure can be used to detect a link that is not
connected to the expected IMA.
FIG. 19 shoWs cases (1, . . . , 7) When the ICP cell
According to a further aspect, the invention is directed to
a method of inverse multiplexing digital data over a con
For a more complete understanding of the invention and
start-up procedure according to one embodiment.
are added to groups With active Link ID=0 links.
multiplexing control cells in a frame, indicating cell stuf?ng.
be transmitted, N being a positive integer and sending a
series of inverse multiplexing control cells indicating a ?rst
speci?c round robin order of the transmission links. The
of ATM data cells according to one embodiment of the
invention.
FIG. 10 is an ICP cell format used for implementing
embodiments of the invention.
FIG. 11 shoWs a circumstance Where node Amay be using
a group of three links to send data to node B and another
group of tWo links to send data to node C.
FIG. 12 shoWs a typical sequence of cells on a three link
group.
FIGS. 13a and 13b shoW an algorithmic ?oW chart for the
FIG. 14 indicates hoW FIGS. 13a and 13b should be
connected.
FIG. 15 shoWs a con?guration When links With Link ID=1
SUMMARY OF THE INVENTION
Brie?y stated, the invention reside in the inverse multi
plexing digital data over a connection consisting of a plu
rality of transmission links, said data containing a series of
ATM data cells. According to one aspect, the invention is
directed to a method of cell stuf?ng to prevent underrun in
a plesiochronous AIM netWork.
In accordance With a yet another aspect, the method
further includes a step of sending tWo consecutive inverse
FIG. 8 is a schematic illustration of multiplexing and
demultiplexing of AIM OAM cells according to one
embodiment of the invention; and
FIG. 9 is a schematic illustration of periodic multiplexing
tion relates to a neW ATM inverse multiplexing scheme that
65
makes use of a physical layer operation administration and
maintenance (OAM) cell Which has been properly de?ned.
This OAM cell is de?ned to contain valuable information to
US 6,205,142 B1
6
5
allow proper operation of the ATM inverse multiplexing
mechanism and also to provide opportunity for handling a
ATM inverse multiplexing remote defect indicator
(AIMRD1)—one octet is allocated and the proposed
coding is all “1”.
ATM inverse multiplexing far-end receiver ready
(AIMFERR)—one octet is allocated and the proposed
coding is all “1”.
ATM inverse multiplexing cell sequence number
link failure situation.
The neWly de?ned OAM cell is called an AIM OAM cell
or AIM Sequence Number (SN) cell and is mainly designed
to carry a cell sequence number and a feedback link status
?eld. The sequence number in the SN cell is made available
for the receiver end for recovering the initial cell stream
from the incoming links. The feedback link status is made
available for the receiver to inform the transmitter, by
sending its oWn SN cells, that it is receiving cells and it is
also an integral part of the same round robin mechanism,
10
(AIMCSN)—it is de?ned to contain the sequence num
ber of the cells sent over the multiple links handled by
the ATM inverse multiplexers. It is designed so as to
have a suf?ciently large cycle to alloW the ATM inverse
multiplexer to absorb link delays of up to 32 millisec
that is to say, the feedback link status value SN cells in either
onds. There are 16 bits allocated to the AIMCSN ?eld.
direction must agree With each other, although the sequence
The counting is then done modulo 65536.
numbers at both ends may be different. When the receiver
sends its oWn SN cells in response to the transmitter that it
15
cell payload. It is proposed to CRC-10 as proposed in
ITU Recommendation 1.432.
is receiving cells, it is in fact acknoWledging that the
receiver is ready to receive subsequent ATM data cells.
Reserve ?eld (R)—contains the octet pattern of
FIG. 4 shoWs hoW the ATM cells are multiplexed and then
demultiplexed over AIMs in one direction. At the transmit
ting node, an AIM 10 takes a series of ATM cells from an
“01101010”, Which is the same as that of the idle cell
as proposed in ITU Recommendation 1.361.
Referring to FIG. 8, the ATM inverse multiplexing pro
ATM layer device. It spreads ATM cells and transmits each
cell over each of N transmission links, N being a positive
integer. The order of transmission is in round robin fashion.
This process is called an inverse multiplexing. At the receiv
tocol according to one embodiment is described in detail
beloW. The ?gure only shoWs one direction for clarity. It is
shoWn that transmission links are all Tl/El links but, of
25
ing node, cells from N links are inverse demultiplexed
proper sequence of cells. Both nodes must be aWare of the
round robin order Which is to be employed. Upon
initialiZation, therefore, both AIMs send a series of SN cells
in round robin fashion over the links, e.g. Tl/El links. This
alloWs the receiver AIM at both nodes to establish the
transmission to a receiving node 26. An AIM at the receiving
node reassembles ATM data cells received from the links in
proper order and sends them to the ATM layer.
Link Start-up
Upon connection start-up, AIMs at both nodes start insert
35
to be transmitted on the virtual link (composed of N physical
links). HoWever, the sequence number is only carried over
the SN cells. This sequence number assignment alloWs the
receiving AIM to retrieve the original cell sequence. The
receiving node queues the received AIM SN cells until it
to the same link round robin. This information can then be
used locally to determine if at the corresponding local node
a link should be added, removed or maintained in the round
robin.
When a change of link con?guration occurs by a link
being added, removed or declared as being doWn, each node
sends a series of SN cells to alloW the far-end node to
45
OAM cell that is de?ned to be exclusively processed by the
determines the sequence in Which to read the ATM data cells
from the incoming links as Well as the differential delay
among individual links. Then, it starts sending AIM SN cells
of its oWn, With the AIMFERR ?eld set to “one” for each
link Which is noW considered “ready” to receive ATM traf?c.
From that moment, the receiving node knoWs the sequence
of cells coming from the links. A link is being considered
available if cells are currently delineated and AIM-RDI is
ATM inverse multiplexers. The neW cell structure has to be
consistent With the cell structure de?ned in ITU Recom
mendation 1.361. FIG. 3 shoWs that structure of UN1/NN1
ATM cells that is de?ned in 1.361. ITU Recommendations
1.361 and 1.432 state that ATM cells consisting of a header
not received on the incoming link.
When the transmitting node starts sending the AIM SN
cells, it starts a time-out of 100 milliseconds Within Which
Whose VPI and VCI ?elds are set to Zero are reserved for use
by the physical layer. So far three preassigned values of the
ing AIM OAM cells (AIM SN cells) carrying cell sequence
number over the available links in round robin fashion. The
sequencing of cells is based on the order in Which cells have
used by each Tl/El link to indicate that both AIMs belong
reestablish the sequence of cells to read from the incoming
links.
The protocol of the invention calls for a physical layer
course, links can have a different speed from Tl/El, as long
as all the links have the same speed. A transmitting node 20
collects digital data consisting of a series of ATM data cells
from the ATM layer. An ATM inverse multiplexer (AIM) at
the transmitting node spreads over multiple links 24 for
(assembled) and sent to an ATM layer device by an AIM 14.
The same order must be employed at this node to recover a
sequence in Which to read cells from the incoming links as
Well as to adjust relative link delay.
As mentioned above, the SN cell also carries an extra ?eld
Cell error control (CEC)—is used to detect errors in the
55
the receiving node determines the sequence of AIM SN cells
Which it is receiving from the links. The time-out expires
cell header are reserved for use by the physical layer. They
unless the transmitting node receives the “ready” signal
are shoWn in FIG. 5.
from all the links Which Were considered available at the
The physical layer OAM cell according to one embodi
ment of the invention is then de?ned by using a non
assigned value by setting the PT ?eld to “111” or some such
code. This is shoWn in FIG. 6.
The A1M OAM cell payload is then available for
initialiZation.
If there is no “ready” link When the time-out expires, the
local node reevaluates the availability of the links (using cell
delineation), starts sending AIM SN cells over the available
links and re-starts the time-out This procedure is repeated
exchanging information betWeen AIMs. The cell payload
until at least one available link is declared ready.
consists of a series of ?elds Whose locations are shoWn in
When the time-out has been cancelled due to the reception
FIG. 7.
65 of the “ready” signal from all the available links, or When
The folloWing ?elds are identi?ed for the AIM protocol
according to one embodiment of the invention:
there is at least one link ready When the time-out expires, the
local end starts sending ATM layer cells over the “ready”
US 6,205,142 B1
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7
link or links using the same round robin order used at the
time of initialization.
Cell Sequence Number Range
Each ATM layer cell gets a sequence number assigned to
it, but only the AIM SN cells carry that number across the
differential delay betWeen individual links of up to 32
milliseconds in one embodiment, and because the system
needs to deal With a maximum of 8 Tl/El links, it is
necessary to have a sequence number Whose modulo is large
Because an ATM inverse multiplexer must absorb a
links. After both nodes have started sending ATM layer cells,
they periodically send a series of “n” AIM SN cells over
links to alloW the receiving node to readjust the differential
enough to accommodate such delay.
As a practical example, the folloWing parameters for E1
delays among the links. The value of “n” is equal to the
number of “ready” links used to carry AIM layer cells. This
means that the receiving node alWays scans for AIM SN
cells in order to determine if it is alWays reading cells from
the multiple links in the correct order. HoW often a burst of
“n” AIM SN cells is sent depends upon the link utiliZation
but the maximum period has been set to 50 milliseconds in
are considered:
full rates: 2.048 Mbit/s
payload rates: 30/32*2.048 Mbit/s=1.92 Mbps
one embodiment. An example of cells sent over a virtual link 15
composed of a plurality of transmission links is shoWn in
FIG. 9.
ATM cell: 53 bytes
ATM cell period time: 221 microseconds
ATM cells/32 milliseconds=144 cells.
For a delay of up to 32 milliseconds on each link, there is
a need to queue cells for at least the same length of time on
Link Recon?guration
tion also deals With link recon?guration. There are three
each link. Therefore, in this example, this means that a delay
of up to a period of 144 cells betWeen tWo links is possible.
An ATM inverse multiplexer can handle a maximum of 8
possible cases in Which recon?guration can occur:
a neW link has to be added to the round robin;
a link has to be intentionally removed from the round
Tl/El links. Therefore up to 1008 cells (144*7 cells) must
be queued at one time by one ATM inverse multiplexer. This
requires a sequence number modulo large enough to cover
As mentioned above, the protocol according to the inven
robin; and
a link has been declared inadequate to provide service
this scenario. A simple case in one embodiment is to use a
25
In the ?rst tWo cases, a node starts link recon?guration by
performing the same initialiZation process for a connection
start-up, that is to say, it chooses a round robin order among
the links and starts sending AIM SN cells using the chosen
round robin order. The receiving node, seeing the occurrence
of AIM SN cells, Will stop transmitting traf?c and starts
sending AIM SN cells of its oWn While adjusting itself to
receive traf?c from the incoming links. The rest of the
protocol is as described earlier for start-up.
TWo possible cases for reporting failure conditions are:
16-bit count that has modulo 65536.
The ATM inverse multiplexing protocol according to the
invention realiZes the folloWing characteristics:
it is applicable to UNIs, BICIs and PNNIs (any applicable
points in an ATM netWork);
it does not affect the ATM cell header of currently de?ned
(eg link doWn by failure etc.).
cells;
it does not require a change to current ATM physical layer
devices dealing With the convergence of ATM cells into
35
Tl/El;
it operates transparently to the ATM layer;
it does not require a change to current devices dealing
1) A medium problem reported through Loss of Delinea
With the processing of the ATM layer cell;
tion (LCD) failure condition. In this case, the corresponding
link should not be used for service. When detecting LCD,
it is self-con?guring among available links upon start-up
and self-recon?guring among the multiple links in the
SN cells With AIMRDI set to “1” should be sent over the
corresponding outgoing link. SN cells containing AIM-RDI
case When a neW link has to be added, deleted or
do not carry a valid sequence number. At the far end, the
considered inadequate to provide service; and
detection of AIM-RDI signals Will indicate that the link is
not to be used. Therefore, if LCD or AIM-RDI is detected,
the link is no longer considered available and Won’t be
alloWed to be part of the round robin on both sides. When
this has happens, SN cells are re-sent over the remaining
links to reestablish the connection betWeen the tWo ends.
2) Cells are lost Without an LCD or AIM-RDI being
reported. For instance, this Would occur When a feW cells are
it includes a sequence number Whose modulo is large
enough to meet the requirement of a large differential
45
delay among the links.
An embodiment of the present invention, involves special
one or more of the previous cells are missing). In this case, 55
Inverse mux Controller Processor (ICP) cells, Which are
more detailed versions of the SN cells. The ICP cell format
is shoWn in FIG. 10. In this embodiment, ATM cells are
transmitted over an N number of links, N being a positive
integer. Cell ID is set for ICP cell and Link ID identi?es links
being used. As seen in FIG. 11, a node A may be using a
group of three links to send data to node B and another group
of tWo links to send data to node C. Nodes A and B form one
IMA group and nodes Aand C form another. IMA groups are
the problem might be partially corrected by re-adjusting the
receiver buffering system (assuming the difference betWeen
identi?ed by IMA ID (Tx and Rx IMA ID). ATM cells on
each link are grouped in a certain number (e.g., M) of cells
the SN cell number and the expected number is small). The
to form IMA frames Which belong to substantially same time
scale. An IMA frame sequence number ?eld counts cells in
discarded by the physical layer device due to bit errors in
cell headers. This Would cause the cell sequencing to be
affected. One symptom Would be the detection of SN cells
Whose number is no longer the same as that expected (since
other symptom Would be the absence of a SN cell on one link
When getting a burst of SN cells on all the other links. In that
case, the local end Would have to force the links to be
re-con?gured. If the symptoms described above reoccur
over a given period, the bad link may have to be removed
from the round robin.
A link recon?guration also occurs When it takes too much
time for one link to receive cells from the far-end (receiving)
node, that is to say, no cells Within, e.g., 32 milliseconds.
each group. FIG. 12 shoWs a typical sequence of cells on a
three link group. One ICP cell is sent at a set location in each
65
group for each link. M can be any number, for example 32,
64, 128 and 256. In the ?gure, on link 0, the ICP cells have
their cell offset set to Zero (i.e., they are the ?rst cell in the
IMA frame). On link 1, the ICP cells have the ICP cell offset
set to 3 and on link 2, the ICP cells have their ICP cell offset
set to 1. In practice, these ICP cells should be distributed
US 6,205,142 B1
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10
even more over the IMA frame but are shown closer for ease
trates looping of a test pattern at node B. The transmit node
receives and veri?es Rx Test Pattern returned over the other
links. It noW knoWs that all the links Which belong to the
of illustration. The ICP cell also includes ?elds concerning
With stuffing action and test control action, both of Which
Will be described in detail beloW.
A status and control change indication ?eld is used to
same IMA group.
FIG. 18 depicts diagrammatically a scenario Where the
test pattern procedure can be used to detect a link that is not
connected to the expected IMA. Links identi?ed as Link
indicate an update of the link status ?eld value. The value is
incremented to indicate a change on at least one of the link
status ?elds. The ?eld is also used as a tag to differentiate
ID=1 are being added to existing groups using links With
Link ID=0. Link 30 carries the IMA B Test Pattern to looped
back by IMAA and links 32 and 34 carry the IMA D Test
link status changes over time. The ?eld Will alWays remain
set to the same value as long as there Will be no change on
any link status ?elds. If one or more link status ?elds need
Pattern to be looped back to IMA B. In this case, the Wrong
test pattern Will be received by IMA B. If IMA B Was not
to be modi?ed, ICP cells With neW link status values
commanding a Test Pattern loopback, IMA B Would simply
incremented Will be sent over all the links.
not receive the right test pattern.
A group status and control ?eld is used to indicate status
The Test Pattern procedure also alloWs to deal With some
of the group of links at a connection start-up, link addition 15
pathological cases. One of them is When tWo IMA connected
and abort procedures. In particular, the start-up procedure
to the same far end IMA node are trying to start-up at the
Would become complicated if one of the links does not meet
same time. The far end (receive end) node Will have to
determine Which set of links (corresponding to one end) it
Wants to be connected to. This Will require the received end
to select the link(s) to be part of the group, as mentioned
above, the receive end shall only respond to one Test Pattern
all the criteria to be part of the group (eg link cleared of
defects, corresponding incoming/outgoing links in loss of
delay synchronization). This requires intervention of the
operator to remove the bad link(s) from the link group.
FIGS. 13a and 13b as combined in the Way shoWn in FIG.
14 shoW an algorithmic ?oW chart for the start-up procedure
according to one embodiment. Instead of requiring all N
number of links in the group being good before starting up,
command at a time that has been validated over one or more
25
links that are or likely to be recogniZed as part of the group.
In accordance With a further embodiment, a stuff cell is
the procedure of the invention proceeds as long as there is
at least P out of N “good” link available for service. A good
inserted to control cell rate decoupling betWeen the links, in
link is de?ned as a link that is not exhibiting link and
each other Within the link groups. The transmitting node
loss-of-frame defects, recogniZed as being part of the group,
and having an acceptable link differential delay. The value of
P could be any number less than N. The ?gure also shoWs
may be locked to one clock source or may be plesiochro
nous. When plesiochronous, one of the buffers at the trans
cases Where the group start-up is aborted and later resumed.
The ICP format also includes a ?eld for links connec
tivity testing at the time of start-up, link addition or link
re-activation. In particular, a protocol must alWays ensure
proper connectivity of the links Which belong to a group. For
example, FIG. 15 shoWs When links With Link ID=1 are
added to groups With active Link ID=0 links. TWo neW links
order to accommodate the use of links non-synchroniZed to
mitting node may be depleted. To prevent underrun, the cell
stuf?ng procedure is invoked. When there is one clock
source, the buffer Will never deplete. The transmitting node
send ICP cells Which indicate a cell is stuffed at a certain
35
location Within the IMA frame. Any cell can be used for
stuf?ng as long as the location is indicated so that the
receiving node can remove it. In actual embodiment, the
transmitting node repeats the ICP cell containing the stuff
code indicating that “this cell is 1 out of 2 stuff cells”. The
receiving node uses the stuff indications over the ICP cells
to determine When to remove stuff cells from the incoming
(Link ID=1 links) are inversely connected With respect to the
expected con?guration. The dif?culty is then that both Link
ID and IMA ID are the same for tWo independent IMAs.
cell stream. The receiving node relies on at least one ICP cell
This can cause an invalid con?guration Which Will not be
With a correct CRC-10. Amore robust approach is to look for
detected. This kind of problem can occur at a start-up, link
a majority of valid codes.
addition or even at a link re-activation. For example, it is
FIG. 19 shoWs cases (1, . . . , 7) When the ICP cell
possible to reactivate a link Which has exhibited a link 45
preceding the stuff event and the stuff ICP cells are cor
failure since it has been accidentally inverted With another
rupted. Corrupted cells are indicated by crosses in the ?gure.
link With or Without the same Link ID and IMA ID. IMA ID
SICP indicate stuf?ng control cells. The receiving node
maintains synchroniZation for cases 1, 2, and 3. The receiv
is also used to detect loopback situations. This problem
occurs When both end nodes of the IMA virtual link Wants
to use the same IMA ID. The invention addresses this
ing node optionally maintain synchroniZation for cases 4, 5,
and 6. The receiving node optionally maintain synchroniZa
problem also.
tion for case 7 if b>2 and When passing stuff indication over
more than one of the previous ICP cells. “b” is the number
According to a further embodiment, the above problems
are solved by sending a test pattern contained in ICP cells
over a link to be validated. The test pattern Will be looped
back over all the other links in the group at the far end node.
of invalid/corrupted ICP cells before declaring the link OIF
55
(out-of-IMA frame).
This ensures that the tested link is connected to the same end
node as the other links.
What is claimed is:
1. A method of inverse multiplexing digital data over a
When one IMA node Wants to determine if one or more
Tx Test control ?eld for link test in an ICP cell. It identi?es
connection consisting of a plurality of transmission links,
said data containing a series of ATM data cells, comprising
steps of:
sending a series of inverse multiplexing control cells
indicating a speci?c round robin order in Which the
Link ID, Tx IMA ID, Rx IMA ID and inserts Test Pattern in
series of ATM data cells are to be transmitted over the
links are connected to the same far end IMA node, it selects
one link for testing. FIG. 16 shoWs the timing diagram of the
test procedure of the invention. The transmit node sets the
the cell. It continues to send same ICPs. The receive end
node receives the ICPs and copies Tx Test Pattern onto Rx
Test Pattern. It keeps sending same test pattern copied on Rx
Test Pattern ?eld over its all outgoing links. FIG. 17 illus
connection;
receiving from the plurality of transmission links a series
of inverse multiplexing control cells Whose receive
ready ?eld is set;